1. Field of the Invention
The present invention relates generally to a telephone set and, more particularly, to an extension phone type cordless telephone allowing radio communication between its terminating set and branch sets.
2. Description of the Related Arts
Most recent developed domestic telephones, for example, are becoming fitted with diverse functions for convenience, amongst which a so-called cordless telephone is rapidly gaining popularity. The cordless telephone set is not fitted with a telephone cord which connects a telephone set body (hereinafter, referred to as a terminating set) associated with a telephone line to a receiver (or a handset). The rapid prevalence of the cordless telephone may have resulted from the telephone user's enlarged action area during a call.
The cordless telephone set can be merely a single terminating set, or a so-called extension phone consisting of a terminating set to which a telephone line is connected and one or more branch sets to which telephone lines are not directly connected.
The former of the cordless telephones generally had the terminating set and a handset separately provided with their respective radio communication circuits, thereby enabling the outside line call to be carried out. The latter of the cordless telephones, that is, the extension type phone, has the terminating set and one or more branch sets separately provided with their respective radio communication circuits, whereby the branch sets are connected to the telephone line of the terminating set through radio communication to allow the branch sets to effect an outside line call, or whereby an extension call can be effected between the terminating set and the branch set through a radio communication, in addition to the outside line call by use of the terminating set.
In the case of such conventional extension phone type cordless telephones having a plurality of branch sets, there may sometimes arise the occasion, while a branch set is in service for an outside call, of wanting to effect an extension call between the terminating set and the other branch set, or while an extension call is busy between a branch set and the terminating set, to effect an outside call by another branch set. In either case, however, the radio communication circuit is inconveniently occupied by the outside line call or the extension call which has priority, so that the other branch set can not effect either an extension call or an outside line call until the completion of such a priority call.
Although it may be conceivable to provide the terminating set with a plurality of radio communication circuits, the radio communication circuit is generally expensive, and the dimensions of the terminating set will be increased if such are provided.